Recording Measured Values

Atop's ability to record measured values proves to be particularly useful. By default it does so every 10 minutes. To change the interval, you either modify the DARGS parameter shown in the first line of Listing 1 in the /etc/init.d/atop init script, or the ExecStart statement from the second line of Listing 1 in the /etc/systemd/system/multi-user.target.wants/atop.service Systemd service file. Change the 600 seconds to the desired value. Alternatively, you can start Atop with a shorter interval whenever needed (e.g.,

atop -w /var/tmp/my-atop.log 10

tells Atop to sample with a 10-scond interval). Pay attention to the storage space usage on the disk.

Atopsar either measures in real time or reports on stored performance data. For example, atopsar -d 1 10 creates 10 measurements of disk usage at intervals of one second. Atop also has the ability to show only the shared resources – this is especially helpful if you have many installed drives, CPUs, or network cards.

With the appropriate options, as summarized in the man page, Atopsar shows reports on processor, memory, and network-related values. If you use the -b and -e parameters to define the start and end times, Atopsar instead parses the current log in /var/log/atop. You can specify another file with -r.

Atopsar also creates reports on a per process basis: For example, -O, -G, -D, or (if you have a patched kernel) -N each show the three processes that use the most CPU time, resident memory, disk I/O, or IPv4/IPv6 network traffic. These reports are not available for live measurements, however.

The ability to interactively browse a logfile with Atop, using the -r option, is also very interesting. You can then view the recorded values as if they were live. Pressing t scrolls forward, and T scrolls back.

Glances

The newcomer among Top programs, the Python-based Glances tool, accesses the psutil library to query system information [8]. On Debian "Jessie" or "Sid," Ubuntu as of 13.04, and Fedora, you simply install the Glances package. The package for SUSE is in the openSUSE build service [9].

The glances command starts the program in normal mode, and glances -s switches to server operation. In this mode, Glances listens for requests on port 61209 for all of the system's IP addresses. The -B option lets you specify an IP address, whereas -p lets you define a different port. The Glances client connects to the server using glances -c <IP address>. The --password option lets you set a password on the server; you need to specify this again when you connect with the client. Whatever option you choose, the system data is transferred unencrypted over the wire.

Even with a terminal size of just 80x24 characters, Glances displays a slew of information: In the header section, you see the CPU and memory usage, as well as the system load (Figure 6). On the left side, the program gives an overview of the network and disk transfer rates, as well as the filesystem fill levels. On the right side, Glances displays the process list. In a larger window, the program gives you additional details in the header and process list, such as some supplementary information on the CPU load, the total CPU time used, or the disk I/O per process.

Figure 6: Compact and informative: Even with 80x24 characters, Glances shows a good deal of information. The Akonadi POP3 resource is stressing a CPU core, but Glances itself uses 5.7 percent as /usr/bin/python.

Pressing c sorts the processes by CPU time, m sorts by memory usage, i by disk I/O, and p by name. As in Atop, pressing a tells Glances to sort by the most commonly used resource. More options for showing and hiding various display elements are revealed by the help feature  (h).

If the window is large enough, Glances shows an event log containing the last three warnings or critical alarms. The configurable limits for the OK, CAREFUL, WARNING, and CRITICAL levels are explained by the documentation. You can export to a CSV file with the following command:

$ glances --output-csv <file>

This gives you an option for importing the values into a spreadsheet. Glances uses a different separator for the column names than for the individual values. Using a comma and the pipe character | gives you a readable import.

Another useful Glances function lets you monitor process groups, which is explained in the documentation below Monitored Processes List.

Conclusions

All of the Top variants discussed here have specific advantages and disadvantages. Glances impresses with its compact view, event log, and (web) server operation. Htop and Top offer extensive configurability in terms of the fields displayed.

My personal favorite is still Atop, however; it shows you precisely the details that are currently relevant and leaves out things that don't really matter. In particular, the logging function, with the ability to create reports and interactively scroll through records, proves to be a big bonus.

pip install glances

pip install --upgrade glances

pip uninstall glances psutil